About Rapid Prototyping

Rapid Prototyping or RP, is a name that is used to describe the process of "printing" a 3D CAD model from an electronic CAD format using Stereolithography. Stereolithography or STL, is a term that describes the layering of material to form an RP part.  STL uses cross-sections of the 3D model at a specified distance from the last cross section and feeds each cross section to a device that adds the material to the prior printed section.  As each layer is printed atop the last until the last cross section, the 3D model is "printed" in the volume of the machine.

Some machines layer atop as the part is lowered in the machine, and some machines print from the bottom as the part is drawn out of the machine. Either way the process is similar.  All prints require some form of support for cross-sections that are too thin on the first pass. Sometimes these supports are wax, or webs added of the same material.

Always, the supports must be removed after printing, and this is called post-processing. 

Most of Keystone details parts are printed in Frosted Ultra Detail (FUD) or Frosted Extreme Detail (FXD).  Both prints use the same material and printing process  The difference is the thickness of each printed cross-sectional layer. One can imagine that the layer thickness has a direct impact on the length of print time in the machine.  It also has a direct affect on the surface quality of the part.

The base material is a fluid that is poured into a vat, and is hardened by the laser upon exposure. With FUD and FXD, a laser is used to print each cross-section.  The laser typically prints the outline of the cross-section first to trap the fluid and then makes a series of cross-hatched movement to harden the trapped fluid. There is usually a percentage of fluid that is not hardened fully during each layer.  As each layer is added the unhardened fluid is trapped in the printout.  Ultraviolet, or UV, light is used to finish curing the print and is the first part of the post-processing.    

The diameter of the laser used also has an impact on the width of of the material that is hardened.  On thin sections and curved surfaces, this is what causes "stepping" or surface striations, similar to a geological map showing elevation change.

FUD and FXD use wax for supports, and the post-processing for these is to use heat to melt away the majority of the supports.  With post processing complete, the RP part is shipped from Shapeways to the customer.


John LeMerise